This invention relates to oil pressure control when a vehicle equipped with an oil pressure clutch and a continuously variable transmission starts running.
Tokkai Hei 8-210449 published by the Japanese Patent Office in 1996 discloses a device for controlling a line pressure supplied to a continuously variable transmission (referred to as CVT hereafter) for vehicles.
The CVT is connected to the engine via a clutch. The line pressure is obtained by adjusting the discharge pressure of an oil pump driven by the engine by a valve.
The line pressure is set according to an input torque of the CVT when the vehicle is running normally.
On the other hand, a basic engaging pressure is set independently to enable the engaging of the clutch in the idle running state of the engine. When a selector lever changes over to a drive range from a neutral range, for example, the control device maintains the line pressure at the basic engaging pressure over a predetermined period from the change-over.
The line pressure not only performs clutch engaging, but also supplies the engaging force required for the clutch to transmit torque and a pressure required for the continuously variable transmission to transmit torque.
If a driver depresses the accelerator pedal, the clutch engaging force required to transmit torque and the pressure required by the continuously variable transmission will also increase.
On the other hand, when the selector lever is changed over to the drive range from the neutral range, the line pressure is maintained at a value corresponding to the basic engaging pressure until a predetermined period elapses. Therefore, if the driver depresses the accelerator pedal in the predetermined period, the clutch can slip without fully obtaining the clutch engaging force required for torque transmission, or an unintended downshift may occur because the continuously variable transmission does not have sufficient pressure.
It is therefore an object of this invention to prevent an insufficiency of line pressure when there are various pressure demands when a vehicle starts.
It is a further object of this invention to quickly and smoothly engage a clutch when a vehicle starts.
In order to achieve the above objects, this invention provides a line pressure control device for such a vehicle that comprises an engine, a continuously variable transmission and a clutch. The transmission and the clutch are connected in series to the engine to transmit a torque according to a line pressure.
The line pressure control device comprises a valve which regulates the line pressure, a sensor which detects a load of the engine, a sensor which detects a torque transmission amount of the clutch, a sensor which detects a speed ratio of the continuously variable transmission, and a microprocessor.
The microprocessor is programmed to calculate a first pressure required for engaging the clutch in an idle running state of the engine, calculate a second pressure required for torque transmission of the continuously variable transmission based on the torque transmission amount of the clutch and the speed ratio of the continuously variable transmission, and control the valve to set the line pressure equal to the first pressure during a first set time from when a supply of the line pressure to the clutch has started, while setting the line pressure equal to a specific pressure based on the second pressure when the load of the engine becomes equal to or greater than a first set value during the first set time.
This invention also provides a control method of a line pressure used by a continuously variable transmission and a clutch connected in series for transmitting a torque generated by an engine of a vehicle.
The method comprises detecting a load of the engine, detecting a torque transmission amount of the clutch, detecting a speed ratio of the continuously variable transmission, calculating a first pressure required to engage the clutch in an idle running state of the engine, calculating a second pressure required for torque transmission of the continuously variable transmission based on the torque transmission amount of the clutch and the speed ratio of the continuously variable transmission, and controlling the line pressure to be equal to the first pressure during a first set time from when a supply of the line pressure to the clutch has started, while controlling the line pressure equal to a specific pressure based on the second pressure when the load of the engine becomes equal to or greater than a first set value during the first set time.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.